Informatica

Sun's nonrepudiation threshold proxy signature scheme is not secure against the collusion attack. In order to guard against the attack, Hwang et al. proposed another threshold proxy signature scheme. However, a new attack is proposed to work on both Hwang et al.'s and Sun's schemes. By executing this attack, one proxy signer and the original signer can forge any valid proxy signature. Therefore, both Hwang et al.'s scheme and Sun's scheme were insecure.

In an internet environment, such as UNIX, a remote user has to obtain the access right from a server before doing any job. The procedure of obtaining acess right is called a user authentication protocol. User authentication via user memorable password provides convenience without needing any auxiliary devices, such as smart card. A user authentication protocol via username and password should basically withstand the off‐line password guessing attack, the stolen verifier attack, and the DoS attack. Recently, Peyravian and Zunic proposed one password transmission protocol and one password change protocol. Later, Tseng et al. (2001) pointed out that Peyravian and Zunic's protocols can not withstand the off‐line password guessing attack, and therefore proposed an improved protocol to defeat the attack. Independently, Hwang and Yeh also showed that Peyravian and Zunic's protocols suffer from some secury flaws, and an improved protocol was also presented. In this paper, we show that both Peyravian and Zunic's protocols and Tseng et al.'s improved protocol are insecure against the stolen verifier attack. Moreover, we show that all Peyravian and Zunic's, Tseng et al.'s, and Hwang and Yeh's protocols are insecure against DoS attack.

We consider a generalized model of neural network with a fuzziness and chaos. The origin of the fuzzy signals lies in complex biochemical and electrical processes of the synapse and dendrite membrane excitation and the inhibition mechanism. The mathematical operations included into fuzzy neural network modeling are: the scalar product between inputs of layers and synaptic weights is replaced by a fuzzy logic multiplication, the sum of products changes to the fuzzy logic sums, and the operators such as supremum, maximum, and minimum are presented for a fuzzy description. The algorithm of varying membership functions, built basing on a backpropagation paradigm and a method of fuzzy neural optimization, has been considered. Both fuzzy properties and a chaos phenomenon are analyzed basing upon experimental computations.

This work describes a realistic performance prediction tool for the parallel block LU factorization algorithm. It takes into account the computational workload, communication costs and the overlapping of communications by useful computations. Estimation of the tool parameters and benchmarking are also discussed. Using this tool we develop a simple heuristic for scheduling LU factorization tasks. Results of numerical experiments are presented.

A partially blind signature scheme allows the signer to inoculate a non‐removable common information into his blind signature. This common information may represent the date or the amount of e‐cash. Due to its un‐traceablility and partial blindness property, the partially blind signature plays an important role in many e‐commerce applications. Based on the RSA scheme, we propose a partially blind threshold signature with low‐computational load for the client.

Identifying legal and illegal states significantly reduces computational complexity of ATPG. A unified framework for identification of the legal and illegal states is presented. Most known methods for identification of the legal and illegal states are interpretable within this framework. New theorems and the resulting procedures for identifying exact collection of legal or illegal states of a circuit are presented. Experimental results demonstrate that exact collection of legal states for some circuits is significantly smaller than collections obtained by backward state search algorithm and by algorithm based on combinational ATPG theorems. The use of the exact collection of legal states allows identifying more undetectable faults. The proposed procedure for identifying of the exact collection of legal states starts from any state of the circuit, builds initially an enlarged collection of legal states and converges rapidly to the exact solution.

Recent publications on multidimensional scaling express contradicting opinion on multimodality of STRESS criterion. An example has been published with rigorously provable multimodality of STRESS. We present an example of data and the rigorous proof of multimodality of SSTRESS for this data. Some comments are included on widely accepted opinion that minimization of SSTRESS is easier than minimization of STRESS.

In the generalized group‐oriented cryptosystem, the sender can send a conditional message to a group of users such that only the specified sets of users in this group can cooperate to decrypt this message. In this paper, we will use an ElGamal cryptosystem and an elliptic curve ElGamal cryptosystem to achieve the purposes of generalization and group‐orientation, respectively. Both of our schemes are more efficient than Tsai et al.'s scheme in terms of sender's computational complexity.

It is a complex non‐linear problem to predict mechanical properties of concrete. As a new approach, the artificial neural networks can extract rules from data, but have difficulties with convergence by the traditional algorithms. The authors defined a new convex function of the grand total error and deduced a global optimization back‐propagation algorithm (GOBPA), which can solve the local minimum problem. For weights' adjustment and errors' computation of the neurons in various layers, a set of formulae are obtained by optimizing the grand total error function over a simple output space instead of a complicated weight space. Concrete strength simulated by neural networks accords with the data of the experiments on concrete, which demonstrates that this method is applicable to concrete properties' prediction meeting the required precision. Computation results show that GOBPA performs better than a linear regression analysis.

A group signature scheme is a digital signature scheme that allows a group member to sign messages anonymously on behalf of the group. Recently, Tseng and Jan proposed two group signature schemes based on self‐certified and ID‐based public keys respectively. However, these two schemes were shown to be insecure against forgery due to Joye et al. Later, Sun et al. showed that Tseng and Jan's self‐certified group signature scheme is linkable. In this paper, we first point out that the proposed linking equation, which is used to check the linkability of Tseng and Jan's self‐certified scheme, cannot work because the inverse problem of RSA is hard. A repaired linking equation is consequently proposed to fix this problem. Then, we show that Tseng and Jan's ID‐based scheme is still linkable because given any two valid group signatures it is easy to decide whether these two group signatures are generated by the same group member or not.